1. Field of the Invention
This invention relates to a high-efficiency displacement fluid machine in which a displacer for moving a working fluid revolves, i.e. makes an orbital motion, with a substantially constant radius relative to the cylinder, into which the working fluid has been drawn, without rotation, thereby conveying the working fluid.
2. Description of the Related Art
As displacement-type fluid machines, there have been long known a reciprocating fluid machine in which a piston is reciprocally moved repeatedly in a cylinder to move a working fluid, a rotary (rolling piston-type) fluid machine in which a cylindrical piston makes an eccentric rotary motion in a cylinder to move a working fluid, and a scroll fluid machine in which a pair of stationary and orbiting scrolls, each having a wrap of a volute configuration formed perpendicularly on an end plate, are engaged with each other, and a working fluid is moved by revolving the orbiting scroll.
The reciprocating fluid machine has an advantage that it can be easily manufactured, and is inexpensive since its construction is simple, but a stroke from the end of the suction to the end of the discharge is as short as 180.degree. in terms of an angle of rotation of a shaft, and the flow velocity during the discharge stroke becomes high, which invites a problem that the performance is lowered because of an increased pressure loss. And besides, since the motion for reciprocating the piston is required, the rotation shaft system can not be perfectly balanced, which invites a problem that large vibrations and noises are produced.
In the rotary fluid machine, a stroke from the end of the suction to the end of the discharge is 360.degree. in terms of an angle of rotation of a shaft, and therefore the problem that a pressure loss increases during the discharge stroke is less serious as compared with the reciprocating fluid machine. However, a fluid is discharged for each rotation of the shaft, and therefore a variation in a gas compression torque is relatively large, which invites vibration and noise problems as in the reciprocating fluid machine.
Various proposals have heretofore been made with respect to a displacement fluid machine of the orbital motion-type (hereinafter referred to as "orbiting fluid machine"). U.S. Pat. No. 385,832 discloses a pump in which a cylindrical displacer makes an orbital motion within a casing, thereby conveying a working fluid. A construction, in which this displacer is formed into a multi-cylinder type, is also disclosed in U.S. Pat. Nos. 406,099 and 940,817. U.S. Pat. No. 801,182 discloses a machine in which a working fluid is compressed not by such a cylindrical-type displacer but by a volute-type displacer. This is an original form of a fluid machine now called "scroll fluid machine", and is a kind of orbiting fluid machine, and these machines have been advanced to such an extent as to form an independent stream.
In such a scroll fluid machine, a stroke from the end of the suction to the end of the discharge is as long as more than 360.degree. in terms of an angle of rotation of a shaft (usually, about 900.degree. in a scroll fluid machine put into practical use for air-conditioning purposes), and therefore a pressure loss during the discharge stroke is small, and besides, generally, a plurality of operation chambers are formed, and therefore there is achieved an advantage that a variation in a gas compression torque is small, so that vibrations and noises are small. However, it is necessary to control a clearance between the volute wraps, engaged with each other, as well as a clearance between the end plate and the tip of the wrap, and therefore high-precision processing or working is needed, which invites a problem that the processing cost is high. And besides, since the stroke from the end of the suction to the end of the discharge is as long as more than 360.degree. in terms of the rotational angle of the shaft, the time for the compression stroke is long, which invites a problem that an internal leakage increases.
Proposed in Japanese Patent Unexamined Publication No. 55-23353 (document 1) and U.S. Pat. No. 2,112,890 (document 2) are a kind of displacement-type fluid machines in which a displacer (orbiting piston) for moving a working fluid revolves, i.e. make an orbital motion, with a substantially constant radius relative to a cylinder, into which the working fluid has been drawn without rotation, thereby conveying the working fluid. The displacement fluid machine, proposed in these publications, comprises the piston of a generally radial shape having a plurality of portions (vanes) extending radially from its center, and the cylinder having a hollow portion similar in shape to the piston. The piston makes an orbital motion within the cylinder, thereby moving the working fluid. These fluid machines are so designed that a pressure pulsation of the working fluid can be reduced so as to reduce a variation in torque, but have not yet matured to a displacement fluid machine sufficiently suited for practical use.
In the structures, disclosed in the above documents 1 and 2, the rotation shaft system can be completely balanced, and therefore, vibrations are small, and also the speed of relative slip between the piston and the cylinder is low, so that a friction loss can be reduced to a relatively small value, which is an essentially advantageous feature for the orbiting fluid machine.
However, the stroke from the end of the suction to the end of the discharge in each of the operation chambers, formed by the plurality of vanes of the piston and the cylinder, is as short as about 180.degree. in terms of the angle .theta. of rotation of the shaft (This is about a half of that of the rotary type, and is about the same as that of the reciprocating type), and therefore the flow velocity of the fluid becomes high during the discharge stroke, so that a pressure loss increases, which invites a problem that the performance is lowered.
And besides, in the fluid machine of this type, a rotation moment, which is produced as a reaction force of the compressed working fluid, and tends to rotate the displacer, is exerted on the displacer, and the vanes of the displacer receive this rotation moment. However, in the structure disclosed in the above documents 1 and 2, the compression operation chambers, formed during the stroke from the end of the suction to the end of the discharge, are disposed in a concentrated manner on one side of the drive shaft, and therefore the rotation moment, acting on the displacer, becomes excessive, so that the vanes are subjected to friction and wear, which invites a problem that the performance and reliability are affected.
Incidentally, taking this drawback into consideration, a fluid machine was actually prepared, and a test was conducted to determine the performance with respect to the rotational speed. As a result, there has been encountered a problem that the compression performance (considered equivalent to the pumping performance) is lowered when the rotational speed exceeds a certain value.